It has already been proposed to insert into two lengths of tubing, which are to be butt joined by welding the ends of these lengths of tubing disposed facing one another and thus defining a junction region, a device comprising sensor means capable of detecting the longitudinal position of one of these ends and centring means capable of centring these two ends relative to one another by bearing, by means of front and rear shoes, on the respective inside walls of each of the two lengths of tubing. In addition, provision has been made to install means, known as welding means, cooperating in carrying out the welding operation and actually consisting of welding heads, between the front arrangement of shoes and the rear arrangement of shoes.
With an arrangement of this kind only little space is available for the installation of the welding means, and in particular it would be impossible to effect electron-beam welding. The method of matching the two lengths of tubing is moreover determined by the need for the front and rear arrangements of shoes to be disposed some distance away from the junction region, and automatic relative centring through the longitudinal thrust of one length of tubing towards the other cannot be contemplated.